1. Field of the Invention
The present invention generally relates to a programmable voltage-controlled oscillator, and more particularly, to a programmable voltage-controlled oscillator which is capable of adjusting the output frequency to approach a predetermined frequency in the process of manufacture.
2. Description of the Prior Art
Along with the popularization of mobile communication products, the wireless structure and the circuit technology are becoming particularly significant. Therefore, in recent years, the miniaturization of the Complementary Metal-Oxide-Semiconductor (CMOS) technology has promoted the radio frequency of MOS component characteristic largely. One example of the CMOS radio frequency improvement is to use low-cost CMOS technology to realize the design of the single crystal transceiver. Thus, it is known that CMOS radio frequency integrated circuit (IC) technology has already made great progress to commercial applications.
Until now, in the circuit design domain (regardless of analogy circuit or digital circuit), a lot of oscillators are usually used for achieving different kinds of signal processing or communication functions. Particularly, one of essential components of wireless communication transceiver is voltage-controlled oscillator (VCO). The voltage-controlled oscillator is one important component that is often used for generating oscillating signal. The principle of the voltage-controlled oscillator is that according to the different reference voltages inputted, the oscillation is carried on by different oscillated frequencies. This characteristic enables the modulation signal to be the inputted voltage-controlled oscillator for generating different modulation signals such as FM modulation, PM modulation and PWM modulation. Although the voltage-controlled oscillator has been developed for a long time, the design of voltage-controlled oscillators is unceasingly been renovating along with the increasing quality of oscillators demanded by modern electronic apparatuses.
However, although the design of the voltage-controlled oscillator is been renovated unceasingly, there are still many problems to overcome in voltage-controlled oscillator. One common question is that in the manufacturing process of voltage-controlled oscillators, due to the limit of material or the difficulty of the process control, the output frequency discrepancy or noise error are generated by the voltage-controlled oscillator. It is thus known that the voltage-controlled oscillator is generally unavoidable to be affected by voltage, temperature and process shift, and so on. Generally speaking, it is impossible that two capacitors experienced the similar manufacturing process have identical capacitance value. Moreover, it is unable for the voltage-controlled oscillator which uses many capacitors to carry on the oscillation with the accurate output frequency. Therefore, how to enable the oscillator which is already completely assembled to successfully control the effective manufacturing rate of the voltage-controlled oscillator is a big challenge.                In this regard, the main domain of the invention is to present a programmable voltage-controlled oscillator that can tune the output frequency to the predetermined frequency in the manufacturing process. Furthermore, with the circuit structure of said programmable voltage-controlled oscillator, the parameter of the programmable voltage-controlled oscillator is able to be adjusted by the control unit in the manufacturing process. In addition, after the control unit adjusts the output frequency to the predetermined frequency, the adjusted programmable code will be burned in the one-time-programming (OTP) component, namely, the fixed output frequency. By doing so, the precision of the output frequency of the programmable voltage-controlled oscillator can be promoted effectively, and its reliability is increased as well.        